Discrete Element Study On The Stability And Support Measures Of Jointed Surrounding Rock Of Underground Cavern

The nature rock mass is usually divided into several parts by weak structureplanes, which not only makes the mechanical properties of rock has been greatlyweakened, but also plays a leading role in deformation and damage mechanism ofrock. Therefore, the design, construction and stability of underground structure shouldtake account of the joints in the rock. In this thesis, based on the diversion tunnel for ahydropower station in western part of China, simulating the tunnel excavation injointed rock by DEM (Discrete Element Method), separately analyzing the influenceof joint characteristics and lateral pressure coefficient on the stability of the cavern.Also has a study on the optimization for support structure of category V softsurrounding rocks of the cavern. The results of this study are listed as follows.（1）The rules and effect of joint dip angle on jointed rock is researched. As thedip angel increases, the displacement of the rock on the roof and the side wall of thecavern increase, which also enforces the distribution of the stresses on the surroundingrocks asymmetry. The higher joint dip angle has a beneficial effect on the bottom ofthe caver, but it has an opposite effect on the side wall of the cavern. The excavationof the cavern in rock masses cut by two set of joints is simulated. Results show thattwo sets of joints has a similar influence on stability of the surrounding rocks with oneset. When the joint sets are vertical, they are likely to keep the rock masses instabilityrelatively. Connectivity rate of joints on the stability is also studied. Poor connectivityof joints has a favorable influence on the stability of the rock, and the area of plasticzone of surrounding rock in discontinuous jointed rock is smaller than connectedjointed rock.（2）The effect of lateral pressure coefficient on the deformation and mechanicscharacteristic of rock is discussed. In case of no support measures, the area of shearzone grows in size with the increase of horizontal in-situ stress, which has an adverseimpact on the stability of surrounding rock. The side wall of the tunnel shows tensileregion with a high lateral pressure coefficient. Therefore, a close attention should betaken to the side wall when the cavern is built in a high horizontal in-situ stressesareas. Strengthen the supporting measures can also be taken into account. （3）Optimization for support measures in the category V soft surrounding rocksis analyzed. When excavating in jointed rock mass, the design of support measuresshould take account of the effects of the support time and thickness of liner on eachother. For the broken rock, the lining structure should be applied in time afterexcavation. Or the lining structure should be designed thicker to increase its bearingcapacity, which can limit the damage in surrounding rock. Owing to the role of rockbolt is to improve the mechanical properties and bearing capacity of the rock, itshould be applied immediately after the excavation.